In- and On-Line Particle Size Distribution Analysis in Highly Concentrated Suspensions and Emulsions

Particle size analysis with ultrasonic extinction from <0.1 - 3,000 µm in real time

Liquid dispersions with a high concentration of solid particles or droplets, often totally opaque, are typically found in production processes. For optical analysers, sampling of a small partial flow of the main product stream combined with a high degree of dilution is required. However, dilution not only causes an extensive preparation effort, but often changes the original state of the dispersion.

For such applications, whose typical range of concentration is between 5 and 50 % by volume, ultrasonic extinction (UE) provides an outstanding performance for particle size distribution analysis of suspension and emulsions. Even paste-like particulate systems with concentrations up to 70 % by volume can be analysed.

Instead of electromagnetic waves (light), ultrasonic extinction applies low energetic sound waves. These waves will be coupled into the sample and run through the sample layer of defined distance. Running through this dispersion layer, part of the sound energy gets absorbed and scattered depending on size and amount of particles or droplets. Sound energy that can pass freely through the sample gets captured by a piezo-electric RF-generator and detector setup. The relation between energy going in and coming out results into a so-called ultrasonic attenuation, which is recorded for 31 frequencies. This frequency dependent attenuation spectrum forms the basis for inverse calculation. This results into a 31 size classes particle size distribution for each of the, as well as information of solid or droplets volume concentrations.

Using sound instead of light waves, ultrasonic extinction is independent of the suspension’s or emulsion’s level of transparency. Hence, totally opaque samples like water droplets in crude oil, mineral slurries or coal particles in pitch can be analysed. Furthermore, materials and products which allow no sampling or dilution without facing destruction due to their stability, rank as standard application.

In addition, the ultrasonic extinction method allows a rugged and robust probe design that resists typical process conditions. The OPUS probe masters temperatures up to 120°C, pressures up to 40 bar and the entire range of pH-value. It is also resistant to aggressive media and abrasive materials. For applications in hazardous atmospheres, an ATEX compliant OPUS version is available.

The process adaptation of OPUS to vessels or to large pipes is simple and typically uses a 100 mm adapter-flange. For smaller pipes or bypass-lines, specific process adapters are available: e.g., flow-through (FT) or bypass (BP). The sensor may be positioned in a standby (SB) rack.

The control and evaluation software using intuitive and high-performance methods provides calculation and display of all relevant and characteristic size distribution values. The OPUS system is fully compliant with FDA requirements and 21 CFR Rule 11. Adaptation to process control systems is natively supported by TCP/IP, Profibus, Modbus, digital or analogue PLC signals.

For many years, OPUS is successfully operating in crystallization, grinding or homogenization processes and proves ultrasonic extinction’s manifold performances. With various applications, OPUS is repeatedly revealing new insights – not only in production lines but also in pilot plants and lab settings.

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